Articles About Calendar (32)
What Is a Calendar?
Calendar definition and meaning: Solar and lunar, tropical and sidereal—why did humans invent calendars?
The Gregorian Calendar
The Gregorian calendar is the internationally accepted civil calendar. It was first adopted in 1582.
The Julian Calendar
The Julian calendar reformed the ancient Roman calendar and consists of three cycles of 365-day years followed by a 366-day leap year.
The Hindu Calendar
Hindus use this calendar to determine the dates of festivals.
The Buddhist Calendar
Buddhists use a lunisolar calendar system. How does it work?
The Islamic Calendar
Muslims around the world use the Hijri calendar. How does it work?
The Jewish Calendar
Jews use the Hebrew calendar to set the dates of religious events.
The Persian Calendar
The Persian Solar Hijri calendar is extremely accurate. Find out why.
The Chinese Calendar
The Chinese calendar is one of the oldest calendars still in use.
The Bah谩始铆 Calendar
The Badi calendar of the Bahai (Bah谩始铆 ) religion features a year of nineteen months. How does the calendar system work?
The Coptic Calendar
The Coptic calendar is linked to the ancient Egyptian calendar and the Julian calendar. It is used in Egypt and in the Coptic Church. How does it work?
The Ethiopian Calendar
The Ethiopian calendar is similar to the Julian calendar.
The Roman Calendar
This is the predecessor to our modern calendar. Some of its features are still in use today.
How Does the Mayan Calendar Work?
The Maya calendar consists of a system of three interlacing calendars and almanacs which was used by several cultures in Central America.
The Revised Julian Calendar
The Revised Julian calendar is one of the most accurate calendar systems ever developed. How does it work, and why don't we use it?
Gregorian Calendar Reform: Why Are Some Dates Missing?
The Gregorian calendar was introduced in 1582 in some countries. The US, Canada, and the UK changed in 1752. Why were some days skipped?
Did the Mayan Calendar Predict The End?
The Mayan calendar ended one of its great cycles in December 2012, fuelling predictions about the end of the world on December 21, 2012 at 11:11(UTC).
About the 12 Months
Why are there 12 months? How long are they, and what do the month names mean?
About the 7 Days
Why are there 7 days? How were the days named, and when does the week start?
What Is a Leap Year?
A leap year has 366 days, as opposed to a common year, which has 365. Nearly every four years is a Leap Year, and we add a leap day, an extra day on February 29.
What Do CE and BCE Mean?
CE is an abbreviation for Common Era and BCE is short for Before Common Era.
Calculating the Easter Date
The date of Easter Day depends on age-old approximations of the Full Moon and the March equinox.
How Accurate Are Calendars?
Our calendar doesn't accurately reflect the time Earth takes to complete a full orbit around the Sun. Why is this? Do other calendars do a better job?
When Did the 21st Century Start?
When did the 3rd millennium and 21st century begin: on New Year's Day 2000 or 2001? Do we count from year 1 or year 0 AD? What century are we in?
The Doomsday Rule
Some dates fall on the same weekday every year. Use this knowledge to calculate the weekday of any given date in your head.
Special Calendar Dates
Learn more about numerically unique calendar dates such as sequential dates, same number dates, and palindrome (reversible) dates
A Year Is Never 365 Days
A tropical year, also known as a solar year, is the time it takes for the seasons to repeat, approximately 365.242189 days.
When Does the Decade Start?
Did the year 2020 mark the beginning of a new decade, or did the twenties begin on January 1, 2021?
How to Write and Count Roman Numerals
Discover how Roman numerals work, as well as the rich history behind them and their use in popular culture.
Holidays Connected to Astronomic Events
People worldwide mark the movement of celestial bodies with a wide variety of celebrations and rituals. We list the most important astronomical holidays.
Thanksgiving Around the World
How do other countries celebrate Thanksgiving? We give you four thankful festivals from Europe, Asia, and Africa.
Valentine鈥檚 Day 2025: A Moon for Lovers
Celebrate love under a glowing Moon! Valentine's Day 2025 is a Full Moon holiday in 29 countries. Find out why a nearly full Moon makes for the perfect romantic night.